In a fuel injection system for a diesel engine, fuel under pressure is supplied directly to the injectors or to a common rail (generally referred to in the following description as a high pressure region) by means of a continuously operating high-pressure pump driven by the engine. The required pressure high injection pressure, which is variable dependent on the engine operating point, is controlled by a valve or metering device of the fuel mass located at the inlet of the high-pressure pump at the low-pressure side of the injection system. The valve or metering device makes sure that the pump delivers the right quantity of fuel to the injectors or the common rail according to the current fuel pressure measured by a sensor arranged at the high pressure side, by applying a closed loop control driven by an electronic control unit.
The metering device is traditionally built as a solenoid valve, and a plunger driven by solenoid force is adapted to free up a metering orifice on the suction side of the pump. Specifically, a fuel flow mass to be delivered by the pump is estimated by the control system dependent on the fuel pressure measured by the sensor as a function of the engine operating mode (e.g., the engine speed as well as other influencing parameters such as fuel and intake-air temperature) and the driver's wishes (e.g., accelerator-pedal setting).
A desired fuel flow mass is obtainable by driving the solenoid valve of the metering device with an actuating signal, specifically an energizing current, which may be determined according to the characteristic of the valve. A nominal characteristic curve of the valve representative of a predetermined relationship between an admissible range of values of an energizing current and the corresponding operating position of the valve (i.e., the fuel flow mass allowed by the metering device, is given by the manufacturer of said device).
In a high pressure system where the fuel pressure is regulated by a valve (metering device) at the inlet of the high pressure pump the electrical characteristics of the valve are fundamental in order to obtain good performances of the control. When the valve has a big production dispersion, the pump characteristic has a big deviation around the nominal characteristic that can cause undershoots and overshoots of the control system during transient conditions, as well as pressure deviations, both positive (i.e., the pressure set-point is higher than the actual pressure) or negative (i.e., the actual pressure is higher than the pressure set-point). These effects not only lead to emissions worsening and noise increasing, but also to the risk of high pressure pump damaging in case of pressure negative deviation.
At least one aim of the present invention is to overcome the drawbacks of the prior art by providing a control method and system for a high pressure pump, which take into account the deviation of the pump characteristic due to production dispersion or ageing. Specifically, it is at least one object of the present invention to develop a strategy for effectively controlling the operating high pressure in a cost-effective fuel injection system equipped with a metering device arranged for regulating the fuel pressure at the inlet of the high pressure system. In addition, other objects, desirable features, and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.